Apparatus and method for space-time coding adaptive to number of antennas in multiple input multiple output wireless communication system

ABSTRACT

Provided is a transmitter apparatus in a MIMO wireless communication system. The transmitter apparatus includes a controller and a space-time encoder. The controller generates a space-time encoding code according to a multiplexing order, the number of transmitter antennas, and the number of receiver antennas. The space-time encoder space-time-encodes a TX signal using the generated space-time-encoding code.

CROSS-REFERENCE TO RELATED APPLICATION(S) AND CLAIM OF PRIORITY

This application claims priority under 35 U.S.C. §119 to an applicationfiled in the Korean Intellectual Property Office on Nov. 1, 2006 andallocated Serial No. 2006-107370, the contents of which are incorporatedherein by reference.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to a multiple input-multipleoutput (MIMO) wireless communication system, and in particular, to anapparatus and method for space-time coding adaptive the number ofantennas in a MIMO wireless communication system.

BACKGROUND OF THE INVENTION

A variety of multimedia services in wireless environments is demanded bythe rapid growth of mobile communication markets. Large-capacity datamust be transmitted at a high speed in order to provide the multimediaservices. Thus, research is being conducted on a multiple input-multipleoutput (MIMO) system for efficiently using limited frequency resources.

Compared to a single-antenna system, the MIMO system can increasetransmission reliability and a data rate without allocating additionalfrequencies or transmit (TX) power. That is, the MIMO system uses adiversity scheme for increasing transmission reliability by achieving adiversity gain according to the number of transmitter (TX) and receiver(RX) antennas, a multiplexing scheme for increasing a data rate bysimultaneously transmitting a plurality of signal sequences, and ahybrid scheme of the diversity scheme and the multiplexing scheme.

In order to achieve a lower error rate, a MIMO wireless communicationsystem uses a space-time coding scheme that extends coding of the timedomain to the space domain. Examples of space-time codes for the MIMOwireless communication system are an Alamouti space-time code for adiversity effect, a BLAST space-time code for a multiplexing effect, anda hybrid space-time code for a trade-off between the diversity effectand the multiplexing effect.

In order to provide a space-time coding scheme suitable for a channelenvironment and the number of usable antennas of a receiver, atransmitter of the MIMO wireless communication system stores all thespace-time codes for a variety of channel environments. Based onfeedback information received from the receiver, the transmitter selectsa suitable space-time code to perform space-time coding.

This, however, complicates the feedback information from the receiverand leads to a waste of memory in the transmitter.

SUMMARY OF THE INVENTION

To address the above-discussed deficiencies of the prior art, it is aprimary object of the present invention is to substantially solve atleast the above problems and/or disadvantages and to provide at leastthe advantages below. Accordingly, an object of the present invention isto provide an apparatus and method for flexibly adjusting diversity ormultiplexing orders in a multiple input-multiple output (MIMO) wirelesscommunication system.

Another object of the present invention is to provide an apparatus andmethod for generating a suitable space-time code by combination ofbasises in a MIMO wireless communication system.

Still another object of the present invention is to provide an apparatusand method for generating a space-time code in a MIMO wirelesscommunication system by using some basises of prestored basisesaccording to the number of usable antennas.

Even another object of the present invention is to provide an apparatusand method for generating a space-time code in a MIMO wirelesscommunication system by using extension basises of prestored basisesaccording to the number of usable antennas.

According to one aspect of the present invention, a transmitterapparatus in a MIMO wireless communication system includes: a controllerfor generating a space-time encoding code according to a multiplexingorder, the number of transmitter antennas, and the number of receiverantennas; and a space-time encoder for space-time-encoding a transmit(TX) signal using the generated space-time-encoding code.

According to another aspect of the present invention, a receiverapparatus in a MIMO wireless communication system includes: a determinerfor determining a multiplexing order using a channel estimation value; acontroller for generating a space-time decoding code according to thedetermined multiplexing order; and a space-time decoder forspace-time-decoding a receive (RX) signal received from a transmitterusing the generated space-time-decoding code.

According to still another aspect of the present invention, a method foran operation of a transmitter in a MIMO wireless communication systemincludes the steps of: generating a space-time encoding code accordingto a multiplexing order, the number of transmitter antennas, and thenumber of receiver antennas; and space-time-encoding a transmit (TX)signal using the generated space-time-encoding code.

According to even another aspect of the present invention, a method foran operation of a receiver in a MIMO wireless communication systemincludes the steps of: determining a multiplexing order using a channelestimation value; generating a space-time decoding code according to thedetermined multiplexing order; and space-time-decoding a receive (RX)signal received from a transmitter using the generatedspace-time-decoding code.

Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, itmay be advantageous to set forth definitions of certain words andphrases used throughout this patent document: the terms “include” and“comprise,” as well as derivatives thereof, mean inclusion withoutlimitation; the term “or,” is inclusive, meaning and/or; the phrases“associated with” and “associated therewith,” as well as derivativesthereof, may mean to include, be included within, interconnect with,contain, be contained within, connect to or with, couple to or with, becommunicable with, cooperate with, interleave, juxtapose, be proximateto, be bound to or with, have, have a property of, or the like; and theterm “controller” means any device, system or part thereof that controlsat least one operation, such a device may be implemented in hardware,firmware or software, or some combination of at least two of the same.It should be noted that the functionality associated with any particularcontroller may be centralized or distributed, whether locally orremotely. Definitions for certain words and phrases are providedthroughout this patent document, those of ordinary skill in the artshould understand that in many, if not most instances, such definitionsapply to prior, as well as future uses of such defined words andphrases.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and itsadvantages, reference is now made to the following description taken inconjunction with the accompanying drawings, in which like referencenumerals represent like parts:

FIG. 1 is a block diagram of a transmitter for a MIMO wirelesscommunication system according to an embodiment of the presentinvention;

FIG. 2 is a block diagram of a receiver for a MIMO wirelesscommunication system according to an embodiment of the presentinvention;

FIG. 3 is a flowchart illustrating a space-time coding procedure in atransmitter for a MIMO wireless communication system according to anembodiment of the present invention; and

FIG. 4 is a flowchart illustrating a space-time decoding procedure in areceiver for a MIMO wireless communication system according to anembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 through 4, discussed below, and the various embodiments used todescribe the principles of the present disclosure in this patentdocument are by way of illustration only and should not be construed inany way to limit the scope of the disclosure. Those skilled in the artwill understand that the principles of the present disclosure may beimplemented in any suitably arranged wireless network.

The present invention is intended to provide a technique for performingspace-time coding in a multiple input-multiple output (MIMO) wirelesscommunication system by flexibly adjusting a diversity order and amultiplexing order according to channel environments and the number ofusable antennas. The diversity order is the number of times ofrepetition of the same signal on the time or frequency axis. Themultiplexing order is the number of signals that can be simultaneouslyreceived by a receiver.

A basis is a basic component that can express all of one space. In abasis set, each basis is linearly independent of other basises and spansa basis space.

The following description is made on the assumption that a transmitterand a receiver of the MIMO wireless communication system each have twoantennas (i.e., 2×2) and diversity and multiplexing orders are adjustedaccording to the combination of basises.

An Alamouti code, a typical diversity code, can be expressed as Equation1:

$\begin{matrix}\begin{matrix}{S_{alamouti} = \begin{bmatrix}s_{1} & s_{2} \\{- s_{2}^{*}} & s_{1}^{*}\end{bmatrix}} \\{= \begin{bmatrix}{\alpha_{1} + {j\; \beta_{1}}} & {\alpha_{2} + {j\; \beta_{2}}} \\{{- \alpha_{2}} + {j\; \beta_{2}}} & {\alpha_{1} - {j\; \beta_{1}}}\end{bmatrix}} \\{= {{\alpha_{1}\begin{bmatrix}1 & 0 \\0 & 1\end{bmatrix}} + {\alpha_{2}\begin{bmatrix}0 & 1 \\{- 1} & 0\end{bmatrix}} +}} \\{{{j\; {\beta_{1}\begin{bmatrix}1 & 0 \\0 & {- 1}\end{bmatrix}}} + {j\; {\beta_{2}\begin{bmatrix}0 & 1 \\1 & 0\end{bmatrix}}}}}\end{matrix} & \left\lbrack {{Eqn}.\mspace{14mu} 1} \right\rbrack\end{matrix}$

In Equation 1, Salamouti denotes an Alamouti code, s_(i) denotes thei^(th) transmit symbol, α_(i) denotes a real value of the i^(th)transmit symbol, β_(i) denotes an imaginary value of the i^(th) transmitsymbol,

$\quad\begin{bmatrix}1 & 0 \\0 & 1\end{bmatrix}$

and

$\quad\begin{bmatrix}0 & 1 \\{- 1} & 0\end{bmatrix}$

denote real basises, and

$\quad\begin{bmatrix}1 & 0 \\0 & {- 1}\end{bmatrix}$

and

$\quad\begin{bmatrix}0 & 1 \\1 & 0\end{bmatrix}$

denote imaginary basises.

The Alamouti code is a diversity code that can provide the maximumdiversity gain. However, as expressed in Equation 1, the transmittertransmits two complex symbols for two time periods using two (2) realbasises and two (2) imaginary basises and thus has a data rate of 1 (=2(the number of transmit (TX) symbols)/2 (transmit (TX) time periods)).That is, a 2×2 MIMO wireless communication system can provide a datarate of 2 by transmitting 4 symbols for 2 time periods, but the use ofthe Alamouti code results in a data rate of only 1 and cannot providethe maximum multiplexing gain for the transmitter and the receiver.

TX symbols of a BLAST code, a typical multiplexing code, can beexpressed as Equation 2:

$\begin{matrix}\begin{matrix}{S_{blast} = \begin{bmatrix}s_{1} & s_{2} \\s_{3} & s_{4}\end{bmatrix}} \\{= \begin{bmatrix}{\alpha_{1} + {j\; \beta_{1}}} & {\alpha_{2} + {j\; \beta_{2}}} \\{\alpha_{3} + {j\; \beta_{3}}} & {\alpha_{4} + {j\; \beta_{4}}}\end{bmatrix}} \\{= {{\alpha_{1}\begin{bmatrix}1 & 0 \\0 & 0\end{bmatrix}} + {\alpha_{2}\begin{bmatrix}0 & 1 \\0 & 0\end{bmatrix}} + {\alpha_{3}\begin{bmatrix}0 & 0 \\1 & 0\end{bmatrix}} + {\alpha_{4}\begin{bmatrix}0 & 0 \\0 & 1\end{bmatrix}} +}} \\{{{j\; {\beta_{1}\begin{bmatrix}1 & 0 \\0 & 0\end{bmatrix}}} + {j\; {\beta_{2}\begin{bmatrix}0 & 1 \\0 & 0\end{bmatrix}}} +}} \\{{{j\; {\beta_{3}\begin{bmatrix}0 & 0 \\1 & 0\end{bmatrix}}} + {j\; {\beta_{4}\begin{bmatrix}0 & 0 \\0 & 1\end{bmatrix}}}}}\end{matrix} & \left\lbrack {{Eqn}.\mspace{14mu} 2} \right\rbrack\end{matrix}$

In Equation 2, S_(blast) denotes a BLAST code, s_(i) denotes the i^(th)transmit (TX) symbol, α_(i) denotes a real value of the i^(th) TXsymbol, and β_(i) denotes an imaginary value of the i^(th) TX symbol.

Basises of the BLAST code can be expressed as Equation 3:

A _(M(τ−1)+m) =B _(M(τ−1)+m)=ξ_(τ)η_(m) ^(t), τ=(1, . . . , T), m=(1, .. . , M).  [Eqn. 3]

In Equation 3, A denotes a real basis in the BLAST code, B denotes animaginary basis in the BLAST code, T denotes the number of transmit (TX)antennas, M denotes the number of receive (RX) antennas, ξ denotes aT-dimensional column vector where only the τ^(th) element is 1 and theremaining elements are 0, and η denotes an M-dimensional column vectorwhere only the m^(th) element is 1 and the remaining elements are 0.

The BLAST code is a multiplexing code that provides the maximummultiplexing gain. In the case of a 2×2 MIMO wireless communicationsystem, both of T and M are 2 in Equation 2. Because there are 8 basises(A=4, B=4), the transmitter and the receiver can provide the maximumdata rate, that is, the maximum multiplexing gain.

As expressed in Equations 1 and 2, the number of basises andcoefficients multiplied by the respective basises vary depending onwhether the code used is the diversity code or the multiplexing code.Therefore, the transmit (TX) symbol matrixes expressed in Equations 1and 2 can be generalized as Equation 4:

$\begin{matrix}{S_{2 \times 2} = {\sum\limits_{i = 1}^{I}{\mu_{i}{A_{i}.}}}} & \left\lbrack {{Eqn}.\mspace{14mu} 4} \right\rbrack\end{matrix}$

In Equation 4, A denotes the basises of a code, μ denotes coefficientsof TX symbols (e.g., α_(i) and β_(i) in Equation 1), and I denotes thenumber of basises of the code (e.g., 4 for the Alamouti code and 8 forthe BLAST code).

That is, the transmitter and the receiver can obtain a space-time codeof desired diversity and multiplexing orders by designing a suitablebasis set and adjusting the number of basises and coefficientsmultiplied by the basises. That is, the diversity or multiplexing ordersare changed by adjusting the value of μ or I in Equation 4.

For example, using 4 basises of

${\gamma \begin{bmatrix}1 & 0 \\0 & 1\end{bmatrix}},{\gamma \begin{bmatrix}0 & 1 \\{- 1} & 0\end{bmatrix}},{\gamma \begin{bmatrix}1 & 0 \\0 & {- 1}\end{bmatrix}},$

and

${\gamma \begin{bmatrix}0 & 1 \\1 & 0\end{bmatrix}},$

and 4 basises of the Alamouti code expressed in Equation 1, a space-timecode can be generated that can provide the maximum diversity gain andthe maximum multiplexing gain in the 2×2 MIMO wireless communicationsystem, as expressed in Equation 5. Herein, γ is a coefficient that ismultiplied to indicate a different basis. If γ is j(√{square root over(−1)}), the code becomes a perfect space-time code (PSTC).

$\begin{matrix}{\begin{matrix}{S_{1} = {{\alpha_{1}\begin{bmatrix}1 & 0 \\0 & 1\end{bmatrix}} + {\alpha_{2}\begin{bmatrix}0 & 1 \\{- 1} & 0\end{bmatrix}} + {j\; {\beta_{1}\begin{bmatrix}0 & 1 \\0 & {- 1}\end{bmatrix}}} + {j\; {\beta_{2}\begin{bmatrix}0 & 1 \\1 & 0\end{bmatrix}}}}} \\{= \begin{bmatrix}s_{1} & s_{2} \\{- s_{2}^{*}} & s_{1}^{*}\end{bmatrix}}\end{matrix}\begin{matrix}{S_{2} = {\gamma \left( {{\alpha_{3}\begin{bmatrix}1 & 0 \\0 & {- 1}\end{bmatrix}} + {\alpha_{4}\begin{bmatrix}0 & 1 \\1 & 0\end{bmatrix}} + {j\; {\beta_{3}\begin{bmatrix}1 & 0 \\0 & 1\end{bmatrix}}} + {j\; {\beta_{4}\begin{bmatrix}0 & 1 \\{- 1} & 0\end{bmatrix}}}} \right)}} \\{= {\gamma \begin{bmatrix}s_{3} & s_{4} \\s_{4}^{*} & {- s_{3}^{*}}\end{bmatrix}}}\end{matrix}{S = {{\begin{bmatrix}s_{1} & s_{2} \\{- s_{2}^{*}} & s_{1}^{*}\end{bmatrix} + {\gamma \begin{bmatrix}s_{3} & s_{4} \\s_{4}^{*} & {- s_{3}^{*}}\end{bmatrix}}} = \begin{bmatrix}{s_{1} + {\gamma \; s_{3}}} & {s_{2} + {\gamma \; s_{4}}} \\{{- s_{2}^{*}} + {\gamma \; s_{4}^{*}}} & {s_{1}^{*} - {\gamma \; s_{3}^{*}}}\end{bmatrix}}}} & \left\lbrack {{Eqn}.\mspace{14mu} 5} \right\rbrack\end{matrix}$

In Equation 5, s_(i) denotes the i^(th) TX symbol, α_(i) denotes a realvalue of the i^(th) TX symbol, β_(i) denotes an imaginary value of thei^(th) TX symbol,

$\begin{bmatrix}1 & 0 \\0 & 1\end{bmatrix},\begin{bmatrix}0 & 1 \\{- 1} & 0\end{bmatrix},{\gamma \begin{bmatrix}1 & 0 \\0 & 1\end{bmatrix}}$

and

$\gamma \begin{bmatrix}0 & 1 \\{- 1} & 0\end{bmatrix}$

are real basises, and

$\begin{bmatrix}1 & 0 \\0 & {- 1}\end{bmatrix},\begin{bmatrix}0 & 1 \\1 & 0\end{bmatrix},{\gamma \begin{bmatrix}1 & 0 \\0 & {- 1}\end{bmatrix}},$

and

$\gamma \begin{bmatrix}0 & 1 \\1 & 0\end{bmatrix}$

are imaginary basises.

That is, by combining the basises as expressed in Equation 5, it ispossible to generate a space-time code with a data rate of 2 thattransmits 4 symbols for 2 time periods.

In the case of a 4×4 MIMO wireless communication system, an example of acode with a data rate of 1 can be expressed as Equation 6:

$\begin{matrix}{M_{{4 \times 4},{{Rate}\; 1}} = \begin{bmatrix}x_{1} & {- x_{2}^{*}} & 0 & 0 \\x_{2} & x_{1}^{*} & 0 & 0 \\0 & 0 & x_{3} & {- x_{4}^{*}} \\0 & 0 & x_{4} & x_{3}^{*}\end{bmatrix}} & \left\lbrack {{Eqn}.\mspace{14mu} 6} \right\rbrack\end{matrix}$

In Equation 6, M_(4×4,Rate1) denotes a space-time code with a data rateof 1 in the 4×4 MIMO wireless communication system and x_(k) denotes thek^(th) TX symbol.

In the code expressed in Equation 6, the real basises are:

$\begin{bmatrix}1 & 0 & 0 & 0 \\0 & 1 & 0 & 0 \\0 & 0 & 1 & 0 \\0 & 0 & 0 & 1\end{bmatrix},\begin{bmatrix}0 & 1 & 0 & 0 \\{- 1} & 0 & 0 & 0 \\0 & 0 & 1 & 0 \\0 & 0 & 0 & 1\end{bmatrix},\begin{bmatrix}0 & 1 & 0 & 0 \\{- 1} & 0 & 0 & 0 \\0 & 0 & 1 & 0 \\0 & 0 & 0 & 1\end{bmatrix},{{and}\begin{bmatrix}1 & 0 & 0 & 0 \\0 & 1 & 0 & 0 \\0 & 0 & 0 & 1 \\0 & 0 & {- 1} & 0\end{bmatrix}},$

and the imaginary basises are:

$\begin{bmatrix}1 & 0 & 0 & 0 \\0 & {- 1} & 0 & 0 \\0 & 0 & 1 & 0 \\0 & 0 & 0 & {- 1}\end{bmatrix},\begin{bmatrix}0 & 1 & 0 & 0 \\1 & 0 & 0 & 0 \\0 & 0 & 0 & 1 \\0 & 0 & 1 & 0\end{bmatrix},{\begin{bmatrix}0 & 1 & 0 & 0 \\1 & 0 & 0 & 0 \\0 & 0 & 1 & 0 \\0 & 0 & 0 & {- 1}\end{bmatrix}\mspace{14mu} {and}},{\begin{bmatrix}1 & 0 & 0 & 0 \\0 & {- 1} & 0 & 0 \\0 & 0 & 0 & 1 \\0 & 0 & 1 & 0\end{bmatrix}.}$

By using the basises of the code expressed in Equation 6, signals can betransmitted through four (4) transmit (TX) antennas to the receiverhaving four (4) receive (RX) antennas. If the receiver has 2 RXantennas, the transmitter extracts some basises from the basises of thecode expressed in Equation 6. If elements of positions (1,1), (1,2),(2,1), and (2,2) are extracted from the basises of the code expressed inEquation 6, the real basises are

$\left. \left\lbrack \begin{matrix}1 & 0 \\0 & 1\end{matrix}\quad \right. \right\rbrack$

and

$\left. \left\lbrack \begin{matrix}0 & 1 \\{- 1} & 0\end{matrix}\quad \right. \right\rbrack$

and the imaginary basises are

$\left. \left\lbrack \begin{matrix}1 & 0 \\0 & {- 1}\end{matrix}\quad \right. \right\rbrack$

and

$\begin{bmatrix}0 & 1 \\1 & 0\end{bmatrix}.$

The extracted basises are a set of basises that can be used in the 2×2MIMO wireless communication system with a data rate of 1.

An example of a code with a data rate of 2 in the 4×4 MIMO wirelesscommunication system can be expressed as Equation 7:

$\begin{matrix}{M_{{4 \times 4},{{Rate}\; 2}} = \begin{bmatrix}x_{1} & {- x_{2}^{*}} & x_{5} & {- x_{7}^{*}} \\x_{2} & x_{1}^{*} & x_{7} & x_{5}^{*} \\x_{3} & {- x_{4}^{*}} & x_{6} & {- x_{8}^{*}} \\x_{4} & x_{3}^{*} & x_{8} & x_{6}^{*}\end{bmatrix}} & \left\lbrack {{Eqn}.\mspace{14mu} 7} \right\rbrack\end{matrix}$

In Equation 7, M_(4×4,Rate2) denotes a space-time code with a data rateof 1 in the 4×4 MIMO wireless communication system and x_(k) denotes thek^(th) TX symbol.

In the code expressed in Equation 7, the real basises are:

$\begin{bmatrix}1 & 0 & 1 & 0 \\0 & 1 & 0 & 1 \\1 & 0 & 1 & 0 \\0 & 1 & 0 & 1\end{bmatrix},\begin{bmatrix}0 & 1 & 1 & 0 \\{- 1} & 0 & 0 & 1 \\1 & 0 & 1 & 0 \\0 & 1 & 0 & 1\end{bmatrix},\begin{bmatrix}1 & 0 & 0 & 1 \\0 & 1 & {- 1} & 0 \\1 & 0 & 1 & 0 \\0 & 1 & 0 & 1\end{bmatrix},\begin{bmatrix}1 & 0 & 1 & 0 \\0 & 1 & 0 & 1 \\0 & 1 & 1 & 0 \\{- 1} & 0 & 0 & 1\end{bmatrix},\begin{bmatrix}1 & 0 & 1 & 0 \\0 & 1 & 0 & 1 \\1 & 0 & 0 & 1 \\0 & 1 & {- 1} & 0\end{bmatrix},\begin{bmatrix}0 & 1 & 0 & 1 \\{- 1} & 0 & {- 1} & 0 \\1 & 0 & 1 & 0 \\0 & 1 & 0 & 1\end{bmatrix},\begin{bmatrix}0 & 1 & 0 & 1 \\{- 1} & 0 & {- 1} & 0 \\0 & 1 & 1 & 0 \\{- 1} & 0 & 0 & 1\end{bmatrix},{{and}\begin{bmatrix}0 & 1 & 0 & 1 \\{- 1} & 0 & {- 1} & 0 \\0 & 1 & 0 & 1 \\{- 1} & 0 & {- 1} & 0\end{bmatrix}},$

and the imaginary basises are:

$\begin{bmatrix}1 & 0 & 1 & 0 \\0 & {- 1} & 0 & {- 1} \\1 & 0 & 1 & 0 \\0 & {- 1} & 0 & {- 1}\end{bmatrix},\begin{bmatrix}0 & 1 & 1 & 0 \\1 & 0 & 0 & {- 1} \\1 & 0 & 1 & 0 \\0 & {- 1} & 0 & {- 1}\end{bmatrix},\begin{bmatrix}1 & 0 & 0 & 1 \\0 & {- 1} & 1 & 0 \\1 & 0 & 1 & 0 \\0 & {- 1} & 0 & {- 1}\end{bmatrix},\begin{bmatrix}1 & 0 & 1 & 0 \\0 & {- 1} & 0 & {- 1} \\0 & 1 & 1 & 0 \\1 & 0 & 0 & 1\end{bmatrix},\begin{bmatrix}1 & 0 & 1 & 0 \\0 & {- 1} & 0 & {- 1} \\1 & 0 & 0 & 1 \\0 & {- 1} & 1 & 0\end{bmatrix},\begin{bmatrix}0 & 1 & 0 & 1 \\1 & 0 & 1 & 0 \\1 & 0 & 1 & 0 \\0 & {- 1} & 0 & {- 1}\end{bmatrix},\begin{bmatrix}0 & 1 & 0 & 1 \\1 & 0 & 1 & 0 \\0 & 1 & 1 & 0 \\1 & 0 & 0 & {- 1}\end{bmatrix},{{{and}\mspace{14mu}\begin{bmatrix}0 & 1 & 0 & 1 \\1 & 0 & 1 & 0 \\0 & 1 & 0 & 1 \\1 & 0 & 1 & 0\end{bmatrix}}.}$

The transmitter extracts some basises from the basises of the codeexpressed in Equation 7. The extracted basises are a set of basises thatcan be used in the 2×2 MIMO wireless communication system.

Thus, a transmitter according to the present invention stores only a setof basises corresponding to the maximum possible number of RX antennas,generates a space-time code by extracting basises according to thenumber of transmitter/receiver (TX/RX) antennas, and performs space-timecoding by using the generated space-time code.

In another embodiment, the transmitter according to the presentinvention stores only a set of basises corresponding to the minimumpossible number of RX antennas, generates a space-time code by extendingbasises according to the number of TX/RX antennas, and performsspace-time coding by using the generated space-time code.

Hereinafter, a description is given of the construction and operationsof a transmitter/a receiver that performs space-time coding/decodingaccording to the above-description principles.

FIG. 1 is a block diagram of a transmitter for a MIMO wirelesscommunication system according to an embodiment of the presentinvention.

Referring to FIG. 1, the transmitter includes an encoder 102, amodulator 104, a demultiplexer (DEMUX) 106, a space-time encoder 108,and a space-time code controller 110.

The encoder 102 encodes a transmit (TX) information bit stream togenerate a coded bit stream. Examples of the encoder 102 include aconvolutional encoder, a turbo encoder, and a low-density parity-check(LDPC) encoder. The modulator 104 modulates the coded bit stream fromthe encoder 102 to generate complex symbols. That is, the modulator 104generates complex symbols by performing signal mapping in aconstellation according to a predetermined modulation scheme. Thedemultiplexer 106 demultiplexes the complex signals from the modulator104 for transmission through a plurality of transmit (TX) antennas. Thespace-time encoder 108 space-time encodes complex symbols received fromthe demultiplexer 106 using a space-time encoding code received from thespace-time code controller 110, and transmits the resulting data throughthe antennas.

The space-time code controller 110 includes a basis generator 112, abasis selector 114, and a code generator 116. Using desired multiplexingorder information, the space-time code controller 110 provides aspace-time encoding code to the space-time encoder 108.

The basis generator 112 generates basises of the size corresponding tothe number of TX/RX antennas from a prestored basis set. The number ofRX antennas of a receiver is information that is known at the initialconnection between the transmitter and the receiver. The basises can begenerated by various methods according to embodiments of the presentinvention. For example, if a basis set corresponding to the maximumpossible number of antennas is prestored, the basis generator 112generates basises by extracting basises according to the number of TX/RXantennas. If a basis set corresponding to the minimum possible number ofantennas is prestored, the basis generator 112 generates basises byextending basises according to the number of TX/RX antennas. If a basisset of a suitable size is prestored, the basis generator 112 generatesbasises by extending or extracting basises according to the number ofTX/RX antennas.

The basis selector 114 determines the number of basises for a space-timeencoding code according to a multiplexing order requested by thereceiver, and selects as many basises as the determined number among thebasises generated by the basis generator 112. The number of the selectedbasises is expressed as Equation 8:

B _(N)=(TX _(MAX,N)×2)/(SM _(MAX,N) /SM).  [Eqn. 8]

In Equation 8, N denotes the number of antennas used, TX_(MAX,N) denotesthe maximum number of symbols that can be transmitted over N timesthrough N antennas, SM_(MAX,N) denotes the maximum multiplexing order inN antennas, and SM denotes a received multiplexing order.

For example, if the multiplexing order is one (1) and the number of theantennas used is two (2), four (=(4×2)/( 2/1)) basises are selected byextracting (2×2)-sized basises from the prestored basises. If themultiplexing order is four (4) and the number of the antennas used isfour (4), thirty-two (=(4×4)/(½)) basises are selected by extending(2×2)-sized prestored basises.

The code generator 116 generates a space-time encoding code using thebasises selected by the basis selector 114, and provides the generatedspace-time encoding code to the space-time encoder 108.

FIG. 2 is a block diagram of a receiver for a MIMO wirelesscommunication system according to an embodiment of the presentinvention.

Referring to FIG. 2, the receiver includes a channel estimator 202, amultiplexing order determiner 204, a space-time code controller 206, aspace-time decoder 214, a parallel-to-serial (P/S) converter 216, ademodulator 218, and a decoder 220.

The channel estimator 202 estimates a channel for each antenna for atransmitter using a predetermined signal such as a pilot signal. Themultiplexing order determiner 204 determines a multiplexing order usingthe channel estimation value received from the channel estimator 202.For example, the multiplexing order may be calculated using the ratio ofthe channel estimation value to the desired data rate of the receiver.Alternatively, the multiplexing order may be calculated using the rankof a channel matrix. The rank of the channel matrix means the number ofrows or columns that are linearly independent, and the channel matrixhas as many non-zero eigenvalues as the rank of the channel matrix. Thesmallest one of the eigenvalues adversely affects the SNR-BERperformance. Thus, the multiplexing order determiner 204 determines amultiplexing order after discarding a small value among the eigenvaluesor setting the same to ‘0’. That is, as the remaining eigenvaluesincrease, the SNR-BER performance increases. In this case, the number ofsimultaneously-transmittable symbols, i.e., a multiplexing orderdecreases and thus a data rate decreases. On the other hand, as amultiplexing order increases, a data rate increases. However, if amultiplexing order is high, TX power must be increased in order tosatisfy a target BER. The multiplexing order information is fed back toa transmitter.

The space-time code controller 206 includes a basis generator 208, abasis selector 210, and a code generator 212. Using the multiplexingorder information received from the multiplexing order determiner 204,the space-time code controller 206 provides a space-time decoding codeto the space-time decoder 214.

The basis generator 208 generates basises of the size corresponding tothe number of TX/RX antennas from a prestored basis set. The number ofRX antennas of the transmitter is information that is known at theinitial connection between the transmitter and the receiver. The basisescan be generated by various methods according to embodiments of thepresent invention. For example, if a basis set corresponding to themaximum possible number of antennas is prestored, the basis generator208 generates basises by extracting basises according to the number ofTX/RX antennas. If a basis set corresponding to the minimum possiblenumber of antennas is prestored, the basis generator 208 generatesbasises by extending basises according to the number of TX/RX antennas.If a basis set of a suitable size is prestored, the basis generator 208generates basises by extending or extracting basises according to thenumber of TX/RX antennas.

The basis selector 210 determines the number of basises for a space-timeencoding code according to the multiplexing order, and selects basisesas many as the determined number among the basises generated by thebasis generator 208. The number of the selected basises is expressed asEquation 8 described above.

The code generator 212 generates a space-time encoding code using thebasises selected by the basis selector 210, generates a space-timedecoding code corresponding to the space-time encoding code, andprovides the generated space-time decoding code to the space-timedecoder 214.

Using the space-time decoding code received from the space-time codecontroller 206, the space-time decoder 214 space-time-decodes signalsreceived through a plurality of antennas. The P/S converter 216 convertsparallel signals received from the space-time decoder 214 into serialsignals. The demodulator 218 demodulates the serial signals receivedfrom the P/S converter 216, thereby generating a coded bit stream. Thedecoder 220 decodes the coded bit stream received from the demodulator218, thereby recovering an information bit stream.

FIG. 3 is a flowchart illustrating a space-time coding procedure in atransmitter for a MIMO wireless communication system according to anembodiment of the present invention.

Referring to FIG. 3, in step 301, the transmitter determines ifmultiplexing order information is received from a receiver.

If the multiplexing order information is received (in step 301), thetransmitter generates basises of the size corresponding to the number ofTX/RX antennas from a prestored basis set, in step 303. The number of RXantennas of the receiver is information that is known at the initialconnection between the transmitter and the receiver. The basises can begenerated by various methods according to embodiments of the presentinvention. For example, if a basis set corresponding to the maximumpossible number of antennas is prestored, the transmitter generatesbasises by extracting basises according to the number of TX/RX antennas.If a basis set corresponding to the minimum possible number of antennasis prestored, the transmitter generates basises by extending basisesaccording to the number of TX/RX antennas. If a basis set of a suitablesize is prestored, the transmitter generates basises by extending orextracting basises according to the number of TX/RX antennas.

In step 305, the transmitter determines the number of basises for aspace-time encoding code according to a multiplexing order requested bythe receiver, and selects basises as many as the determined number amongthe basises generated in step 303. For example, the number of theselected basises is expressed as Equation 8 described above.

In step 307, the transmitter generates a space-time encoding code usingthe selected basises.

In step 309, the transmitter space-time-encodes signals using thegenerated space-time encoding code, and transmits the space-time-encodedsignal to the receiver.

FIG. 4 is a flowchart illustrating a space-time decoding procedure in areceiver for a MIMO wireless communication system according to anembodiment of the present invention.

Referring to FIG. 4, in step 401, the receiver estimates a channel foreach antenna for a transmitter using a predetermined signal such as apilot signal.

In step 403, the receiver determines a multiplexing order using thechannel estimation value in step 401. For example, the multiplexingorder may be calculated using the ratio of the channel estimation valueto the desired data rate of the receiver. Alternatively, themultiplexing order may be calculated using the rank of a channel matrix.The receiver feeds the multiplexing order information back to atransmitter.

In step 405, the receiver generates basises of the size corresponding tothe number of TX/RX antennas from a prestored basis set. The number ofRX antennas of the transmitter is information that is known at theinitial connection between the transmitter and the receiver. The basisescan be generated by various methods according to embodiments of thepresent invention. For example, if a basis set corresponding to themaximum possible number of antennas is prestored, the receiver generatesbasises by extracting basises according to the number of TX/RX antennas.If a basis set corresponding to the minimum possible number of antennasis prestored, the receiver generates basises by extending basisesaccording to the number of TX/RX antennas. If a basis set of a suitablesize is prestored, the receiver generates basises by extending orextracting basises according to the number of TX/RX antennas.

In step 407, the receiver determines the number of basises for aspace-time encoding code according to the multiplexing order determinedin step 403, and selects basises as many as the determined number amongthe basises generated in step 405. For example, the number of theselected basises is expressed as Equation 8 described above.

In step 409, the receiver generates a space-time encoding code using theelected basises, and generates a space-time decoding code correspondingto the space-time encoding code.

In step 411, using the space-time decoding code generated in step 409,the receiver space-time-decodes signals received through a plurality ofantennas.

In the above embodiment, the receiver generates its space-time decodingcode in the same method as for the transmitter. In another embodiment,the transmitter generates a space-time encoding code and provides(feedforwards) the space-time encoding code or a space-time decodingcode to the receiver, and the receiver performs space-time decodingusing the feedforward code information.

In the above embodiment, the transmitter selects basises for aspace-time encoding code using the multiplexing order informationreceived from the receiver. In another embodiment, the receivertransmits channel state information to the transmitter, and thetransmitter determines the multiplexing order based on the channel stateinformation received from the receiver.

Although the present disclosure has been described with an exemplaryembodiment, various changes and modifications may be suggested to oneskilled in the art. It is intended that the present disclosure encompasssuch changes and modifications as fall within the scope of the appendedclaims.

1. A transmitter apparatus in a multiple input-multiple output (MIMO)wireless communication system, the apparatus comprising: a controllerfor generating a space-time encoding code according to a multiplexingorder, the number of transmitter antennas, and the number of receiverantennas; and a space-time encoder for space-time-encoding a transmitsignal using the generated space-time-encoding code.
 2. The transmitterapparatus of claim 1, wherein the multiplexing order is received fromthe receiver.
 3. The transmitter apparatus of claim 1, wherein themultiplexing order is determined in the transmitter using a channelinformation received from receiver.
 4. The transmitter apparatus ofclaim 1, the multiplexing order is calculated using the ratio of thechannel estimation value to the desired data rate of the receiver in thetransmitter or receiver.
 5. The transmitter apparatus of claim 1,wherein the multiplexing order is the number of signals that can bereceived in the same time.
 6. The transmitter apparatus of claim 1,wherein the controller comprises: a basis generator for generatingbasises according to the number of the transmitter antennas and thenumber of the receiver antennas; a basis selector for determining thenumber of basises according to the multiplexing order and selectingbasises as many as the determined number; and a code generator forgenerating the space-time encoding code using the selected basises. 7.The transmitter apparatus of claim 6, wherein the basis generatorgenerates the basises by extending basises included in a prestored basisset according to the number of the transmitter antennas and the numberof the receiver antennas.
 8. The transmitter apparatus of claim 6,wherein the basis generator generates the basises by extracting basisesfrom basises included in a prestored basis set according to the numberof the transmitter antennas and the number of the receiver antennas. 9.The transmitter apparatus of claim 1, wherein the controller providesthe space-time encoding code information to the receiver.
 10. A receiverapparatus in a multiple input-multiple output (MIMO) wirelesscommunication system, the apparatus comprising: a determiner fordetermining a multiplexing order; a controller for generating aspace-time decoding code according to the determined multiplexing order;and a space-time decoder for space-time-decoding a receive signalreceived from a transmitter using the generated space-time-decodingcode.
 11. The receiver apparatus of claim 10, wherein the determinerdetermines the multiplexing order using the channel estimation valueitself.
 12. The receiver apparatus of claim 10, wherein the determinerdetermines the multiplexing order received from the transmitter.
 13. Thereceiver apparatus of claim 10, wherein the multiplexing order is thenumber of signals that can be simultaneously received by the receiver.14. The receiver apparatus of claim 10, wherein the controller generatesbasises according to the number of transmitter antennas and the numberof receiver antennas, selects one or more basises from the generatedbasises according to the multiplexing order, and generates thespace-time decoding code using the selected basises.
 15. The receiverapparatus of claim 10, wherein the controller generates the space-timedecoding code by detecting space-time decoding code information fed backfrom the transmitter.
 16. The receiver apparatus of claim 10, whereinthe determiner determines the multiplexing order using the ratio of thechannel estimation value to the desired data rate of the receiver. 17.The receiver apparatus of claim 10, wherein the determiner provides themultiplexing order information to the transmitter.
 18. A method for anoperation of a transmitter in a multiple input-multiple output (MIMO)wireless communication system, the method comprising: generating basisesaccording to the number of transmitter antennas, and the number ofreceiver antennas to generate a space-time encoding code; generating aspace-time encoding code according to a multiplexing order by using thegenerated basises; and space-time-encoding a transmit signal using thedetermined space-time-encoding code.
 19. The method of claim 18, whereinthe multiplexing order is received from the receiver.
 20. The method ofclaim 18, the multiplexing order is calculated using the ratio of thechannel estimation value to the desired data rate of the receiver. 21.The method of claim 18, wherein the basises are generated by extendingbasises included in a prestored basis set according to the number of thetransmitter antennas and the number of the receiver antennas.
 22. Themethod of claim 18, wherein the basises are generated by extractingbasises from basises included in a prestored basis set according to thenumber of the transmitter antennas and the number of the receiverantennas.
 23. A method for an operation of a receiver in a multipleinput-multiple output (MIMO) wireless communication system, the methodcomprising: determining a multiplexing order; generating a space-timedecoding code according to the determined multiplexing order; andspace-time-decoding a receive signal received from a transmitter usingthe generated space-time-decoding code.
 24. The method of claim 23,wherein the multiplexing order is determined by using the channelestimation value.
 25. The method of claim 23, the multiplexing order isreceived from the transmitter.